1. Field of the Invention
The present invention relates to an optical film with a reinforced layer, particularly to the optical film with superior in thermal stability, dimensional stability and anti-deformation ability.
2. Description of Related Art
With the advancement of technology, in order to meet people's needs for light, thin, short and small electronic digital products, it prompted the development of the thickness of liquid crystal display panel to become thinner and more lightweight so as to achieve a lightweight and thin electronic digital products which are easy to carry. An efficient way to achieve this goal is to make the backlight module thinner.
The fundamental structure of a common backlight module except the light source includes (from bottom to top): reflective sheet, light guiding plate, lower diffusion sheet, lower luminance enhancement film, upper luminance enhancement film and upper diffusion sheet. In order to reduce the thickness of the backlight module, the existing methods in the industry are as follow: (1) using a multi-functional composite sheet material, i.e., integrating parts of the optical films mentioned above into one composite sheet, for example, combining the upper diffusion sheet with upper luminance enhancement film into one upper luminance enhancement composite sheet; (2) reducing the thickness of each optical film, and thus achieving the purpose of reducing the total thickness thereof, for example, changing the luminance enhancement film used for notebook computers from the original substrate whose thickness is 125 μm into the replaced substrate whose thickness is 100 μm, or even 75 μm.
However, in adopting the above-mentioned method (2), particularly using the substrate with thinner thickness, there would be the following problem. When, using a substrate with, a large area to produce a large-size panel, the rigidity of the substrate will become insufficient and thus easily cause deformation. In addition, when the light source of the backlight module is of edge light, the heat is easy to concentrate on the specific location at the edge of the backlight module, causing that the temperature at the edge of the backlight module would be higher than that in other portion of the backlight module and then making the edge of the substrate easily deform due to the high temperature, thereby re-suiting in some problems, such as warp, corrugation, unevenness. This problem would be more apparent on the substrate with thinner thickness.
As to prior arts about applying coating layer on the specific layer of the backlight module to achieve unique purposes, there are some examples as follows.
First, U.S. Pat. No. 5,995,288 (hereinafter, referred to as “PD1”) discloses an optical sheet in which a resin coating layer is disposed on a side of the substrate opposite to the side forming unit prisms. The coating layer has a thickness in the range from 2 μm to 20 μm and contains particles whose particle diameter is in the range from 1 μm to 10 μm, whereas the ratio of the refractive index of the particles to the refractive index of the resin forming the coating layer is in the range from 0.9 to 1.1. With this structure, a purpose for preventing the Newton's rings can be achieved.
In addition, U.S. Pat. No. 6,280,063 (hereinafter, referred to as “PD2”) discloses a brightness enhancement article in which a first major surface of the substrate forms an array of prisms while a second major surface of the substrate forms a light scattering layer. This light scattering layer has a thickness in the range from 1 to 50 μm and contains a plurality of components projecting from the second major surface. Additionally, the haze value of this brightness enhancement article is in the range from 20 to 60% and transmittance is not greater than 94%, whereby the brightness enhancement article can maintain a brightness enhancement characteristic and an extinction characteristic as well.
Furthermore, US 2008/0151549 (hereinafter, referred to as “PD3”) discloses a scratch-resistant optical film in which a hard coating layer is provided on the surface of the reflective substrate as a scratch-resistant layer. The scratch-resistant, layer has a surface resistivity in the range from 108Ω/□ to 1012Ω/□, a thickness in the range from 1 μm to 20 μm; and contains organic particles whose particle diameter is in the range from 0.1 μm to 10 μm. Based on this structure, the reflective substrate has low shrinkage ability, hardly warps and has a good antistatic and high hardness, wherein the reflective substrate may have excellent scratch resistance due to the high hardness.